Damage evaluation in discontinuously reinforced aluminum matrix composites subjected to thermal cycling

A comparative study of the damage in the powder metallurgy processed Al-Cu-Mg alloy-SiC (as-extruded and solution-treated) and Al-SiC (hot rolled), and in situ cast Al-TiC (as-extruded) composites, each with 15 vol.% particulate reinforcements, has been carried out. Repeated thermal cycling of the composites between 500 and 0 °C was followed by evaluation of damage by examination of microstructure using scanning electron microscopy, determination of changes in dynamic Young's modulus, and measurement of microhardness near the reinforcement-matrix interfaces. The thermally cycled Al alloy-SiC composites have exhibited reduction in Young's modulus and microhardness adjacent to reinforcement-matrix interfaces, due to decohesion caused by thermal mismatch strains. In contrast, the SiC or TiC reinforced Al composites subjected to thermal cycling, have shown only a marginal reduction in the Young's modulus, and cracks in the Al matrix rather than at interfaces, near which microhardness increment by strain-hardening through dislocation generation has been noticed.